A verse no5 well considered. Yes, Paul was bitten by a snake and he lived but is that what is being spoken in this single verse?
17 And the seventy turned back with joy, saying, `Sir, and the demons are being subjected to us in thy name;'
18 and he said to them, `I was beholding the Adversary, as lightning from the heaven having fallen;
19 lo, I give to you the authority to tread upon serpents and scorpions, and on all the power of the enemy, and nothing by any means shall hurt you;
20 but, in this rejoice not, that the spirits are subjected to you, but rejoice rather that your names were written in the heavens.'
I say all of the time but here it is again:
In the Bible, no scripture, collection of scriptures nor passage of sccripture can ever be fully understood without the clear light of all scripture shinning on it/them!
Lets begin, Verse 17 begins the thought with the action of the seventy, the following of Jesus at that time returning to report the results of their efforts to complete the mission in the cause of Jesus. That places this discussion, directly, into the Spiritual Realm, the realm we, as members of the body, are called to work in. They were so into the Spitiual Work, they were so trusting God that though they were a little lower than the Angels (Heb. 2:7) They were telling the evil Angles what to do in the name of Jesus. Then, in verse 18, Jesus responds now and the subject He speaks of in this sentence as our Adversary. Jesus is speaking of That Old Dragon, Satan, here and not of Copperheads, Diamond Backs, or Eastern Rattle Snakes.
Finally in verse twenty, He indicate that what a portion of the Church is involved in, is to Him, nasty, unholy! We have, in our midst, Churches that Glorify themselves with the handling of all manor of snake and God/Jesus warned us in this passage not to tempt Him that way.
Actually, this, just as the Parables Jesus did not explain are for him that hasw the ears to hear, spiritual ears!